The invention relates to a method for providing virtual and backup metering, surveillance and injection control of a cluster of injection wells and/or injection wells with multiple zones and/or branches, used for the injection of fluids into underground reservoirs.
In many oil production operations, where oil is produced from underground reservoirs, various fluids are injected into the reservoirs to increase recovery of oil. The injected fluids increase oil recovery by providing increased pressure support for the extraction of oil, or by displacing the oil toward the wells. Typical fluids injected into the reservoirs for IOR operations include water or hydrocarbon gas. In the state of the art for Improved Oil Recovery (IOR) operations, each injection well may furthermore have multiple injection zones or branches for which the injection flow into each zone and/or branch is to be monitored and controlled.
Additionally, in many oil production operations, effluents are produced as by-products of the oil and gas extraction process, and such waste effluents are disposed off by injection into reservoirs via disposal wells. Typically, the effluents disposed into underground reservoirs include excess produced water or carbon dioxide. The reliability of such disposal operations is often critical for the simultaneous oil and gas production process. Similarly, injection wells are also found in underground storage operations in which hydrocarbon gas is stored in underground locations.
In the above cases, the process of injection into underground formations requires surveillance and control to monitor the amount of the effluents injected and to adjust the injected flows consistent with the objectives of the process, for example to ensure a uniform sweep of oil bearing formations. Furthermore, surveillance is required to ensure detect changes in the receptiveness of the well and reservoir to continued injection, either due to injection well impairment, fractures in the reservoir matrix or due to increased reservoir pressures.
In conventional practice, injection wells are often equipped at the surface with single phase flow meters and pressure measurements. However, flowmeters are susceptible to drift in accuracy or of complete failure. For example, water flow meters tend to scale up. It is not abnormal in the field for the sum of individual water meter measurements to be very significantly different from the measurement of the total water flow before distribution to the individual wells. In the case of meter failures, a computer algorithm or “Virtual Meter” may be generated to provide an alternative substitute estimates for the injected flows. Similarly, it is desirable to provide a method for validation and reconciliation of the injection flows or estimates. In additional to the foregoing, in the case of injection wells with multiple injection zones and/or branches, it is in general problematic to provide subsurface flow meters to measure injection flows into individual zones and/or branches. In such cases, virtual flow meters may be applied for tracking of injection into each individual zone or branch.
Applicant's International patent application PCT/EP2005/055680, filed on 1 Nov. 2005, “Method and system for determining the contributions of individual wells to the production of a cluster of wells” discloses a method and system named and hereafter referred to as “Production Universe Real Time Monitoring” (PU RTM). The PU RTM method allows accurate real time estimation (virtual metering) of the multiphase oil, water and gas contributions of individual wells to the total commingled production of a cluster of crude oil, gas and/or other fluid production wells, based on real time well measurement data such as well pressures, in combination with well models derived from data from a shared well testing facility and updated regularly using reconciliation based on comparing the dynamics of the well estimates and of the commingled production data.
Applicant's International patent application PCT/EP2007/053345, filed on 5 Apr. 2007, “METHOD FOR DETERMINING THE CONTRIBUTIONS OF INDIVIDUAL WELLS AND/OR WELL SEGMENTS TO THE PRODUCTION OF A CLUSTER OF WELLS AND/OR WELL SEGMENTS” discloses a method and system named and hereafter referred to as “PU RTM DDPT”. The PU RTM DDPT, used in association with the method of PU RTM, allows the accurate real time estimation of the contributions of individual wells, using well models based on data derived solely from the metering of commingled production flows and the dynamic variation of flow therein, without the use of a well testing facility. The PU RTM DDPT method is specifically applicable and necessary for production wells with multiple zones and/or branches, and wells without a shared well test facility, such as subsea wells sharing a single pipeline to surface production facilities. Further, the Applicant's International patent application PCT/EP2007/053348, filed on 5 Apr. 2007, “METHOD AND SYSTEM FOR OPTIMISING THE PRODUCTION OF A CLUSTER OF WELLS” discloses a method and system named and hereafter referred to as “PU RTO”. The PU RTO, used in association with the method of PU RTM, provides a method and system to optimise the day to day production of a cluster of wells on the basis of an estimation of the contributions of individual wells to the continuously measured commingled production of the cluster of wells, tailored to the particular constraints and requirements of the oil and gas production environment.
It is an object of the present invention to extend the concepts of the above inventions to provide a method, which supports the backup metering and reconciliation of flows into injection wells, including injection flows into individual zones and/or branches of injection wells, and the control of downhole pressures in, and of injection rates into, individual zones and/or branches of suitably equipped injection wells. In particular, the PU RTM DDPT method of characterizing wells which do not have access to shared well testing facilities is applied to injection wells, as such wells do not have access to shared well testing facilities.
It may also be noted that the relevant prior art includes approaches which use conventional thermodynamic and fluid mechanics models from chemical engineering or physics to track flows, for example the reference “Belsim Data Validation Technology” dated 9 Dec. 2004, retrieved from the internet at www.touchbriefings.com/pdf/1195/Belsim_tech.pdf. Such methods have the difficulty that technically complex a priori models need to be set up. This approach is thereafter difficult to sustain in practice as various physical and fluid parameters change. These approaches are also usually based on daily totals and do not incorporate the pattern reconciliation of the PU RTM invention. The present invention is based on the practical use of minute by minute actual field data from simple field testing, building from the PU RTM DDPT approach, to construct and regularly systematically update models for the backup metering and for the reconciliation of injection flows.